In the field of photographic platemaking there is a need for photographic materials with good original reproducibility, stable processing solutions and an adequate simplification to cope with the complexity and the diversity of printing materials.
In particular, the original in a line photographic process is produced by plating photo-setting characters, handwritten characters, illustrations, halftone photographs and the like. Images with different densities and line widths are therefore intermixed in the original, and there is therefore a strong need for a platemaking camera, photographic materials and image-forming methods which foithfully reproduce such originals. Meanwhile, enlargement and reduction of the halftone photograph is widely undertaken in platemaking for catalogs and large posters, resulting in photographs with faded dots and coarsening in the line numbers in platemaking using enlargement of halftones. Reduction results in a photograph with a larger number of lines per inch and finer dots than the original. There is therefore a demand for an image-forming method with a much wider latitude in order to preserve the reproducibility of the halftone gradation.
Halogen lamps and xenon lamps are used as the light sources for platemaking cameras. The photographic material is usually orthochromatically sensitized in order to achieve the photographic speed for such light sources. However, orthochromatically sensitized photographic materials are more strongly affected by the differential color absorption of the lens, and it will be seen that the image quality is therefore likely to deteriorate. Furthermore, this deterioration is more pronounced with xenon lamp light sources.
One system which is intended to meet the demand for a wider latitude is a method in which a lithographic silver halide photosensitive material consisting of silver chlorobromide (with a silver chloride content of at least 50%) is processed in a hydroquinone developing solution with a highly reduced effective concentration of sulfite ions (normally 0.1 mole/1 or less) to produce a line image or halftone image in which the image portion and the non-image portion are clearly separated and with a high contrast and high black density. However, at present, because of reduced sulfite concentration in the developing solution in this method, the developing solution is extremely unstable to atmospheric oxidation despite many attempts to keep the solution activity stable. Further, the processing speed is decidedly slow and the operating efficiency is low.
There is therefore a need for an image-forming system which overcomes the instability of image formation in a developing method (lithographic developing system) as has been described above, allows development in a processing solution with good storage stability and with which an ultra-high contrast photographic characteristic is obtained. There have been proposals for systems which form ultra-high contrast negative images with gammas of more than 10 which involve processing a surface latent image type silver halide photographic material to which a specific acylhydrazine compound has been added in a developing solution having a good storage stability and containing 0.15 mole/l or more of sulfite preservatives at a pH of 11.0 to 12.3, as can be seen from U.S Pat. Nos. 4,166,742, 4,168,977, 4,221,857, 4,224,401, 4,243,739, 4,272,606 and 4,311,781. Whereas only silver chlorobromides with a high silver chloride content could be used in conventional high-contrast image formation, this image-forming system has the distinguishing feature that silver iodobromide and silver chloroiodobromide can also be used.
The above image systems exhibit outstanding properties in their sharp halftone quality and their processing stability, rapidity and the reproducibility of the original, but there is a need for a system with even better original reproducibility in order to cope with the recent diversity of printing materials.
JP-A-61-213847 (the term "JP-A" as used herein means an "unexamined published Japanese Patent Application") and U.S. Pat. No. 4,684,604 disclose photographic materials which contain redox compounds which release photographically useful groups upon oxidation and disclose attempts at broadening the range of gradation reproduction. However, in ultra-high contrast processing systems employing hydrazine derivatives, these redox compounds have the disadvantage that they impair greater contrast and it has not been possible to take full advantage of their characteristics.